The present invention relates to a method of manufacturing a semiconductor device, and more particularly to an X-ray exposure method for transferring mask patterns onto a substrate by using a soft X-ray.
The X-ray exposure method is a semiconductor manufacturing process in which a mask consisting of an X-ray transmissible support film and absorbing patterns is irradiated with soft X-rays to transfer desired patterns onto a substrate by light transmitted through the mask. Since the soft X-ray has a wavelength two orders of magnitude shorter than an ultraviolet light which is used for a conventional light exposure method, it can reduce the influence of Fresnel diffraction and obtain a high resolution.
However, even with the X-ray exposure method, the influence of Fresnel diffraction causes deterioration in resolution in a sub-micron region. For this reason, for example, as discussed in "Micrelectronic Engineering", vol. 9, pp. 127-130, 1989 by Hasegawa et al, and JP-A-2-52416, trials have been made for improving the resolution by utilizing an interference effect of X-rays. These trials are featured by working side walls of an absorbing pattern 5 which has conventionally been rectangular as shown in FIG. 1a to a tapered shape 8 or the like as shown in FIG. 1b in order to change a optical path length of an X-ray. As a result, the phase of an X-ray 9 transmitted through the side walls of the absorbing pattern is advanced with respect to an X-ray 6 from an ordinary transmitting portion and interferes with expansion of an exposure intensity of the X-ray 6 due to Fresnel diffraction, whereby a distribution of exposure intensity by the transmitted X-rays is made abrupt, thereby making it possible to achieve the improvement of resolution.
In commonly assigned U.S. application Ser. No. 07/593808, filed Oct. 5, 1990, a technique is disclosed wherein, after forming a light shield film having a predetermined shape on a glass substrate, a flattening layer for flattening a difference in level of the light shield film, and a phase shifter is formed thereon.